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Bank8:Risk — README

Prudential risk measurement: capital (Basel), liquidity (LCR/NSFR), credit (IFRS 9 ECL), market, and operational risk, plus stress testing and limit monitoring — a continuous measurement engine that consumes posting/transaction events and emits limit-breach events, never moving money itself.

Summary​

Bank8:Risk is a Rust service owning the risk schema in the bank8 vertical database. It continuously measures exposures, capital components, liquidity buffers, expected credit losses, and stress scenario outcomes from the events and balances Bank8:Ledger and Bank8:Payments produce, monitors them against configured limits, and emits bank8:risk:limit:breached events when a limit is crossed. It feeds Bank8:Reporting (filing inputs) and is itself read via public API.

Motivation​

Risk obligations are continuous, not batch: capital adequacy, liquidity coverage, credit loss, and limit headroom must be known at any moment, not only at filing time. A dedicated measurement service keeps the money-movement hot path (Ledger/Payments) free of risk computation, and emits breaches as events so Compliance (alerting) and Reporting (filing) react without a bespoke internal API.

Architecture & High-Level Design​

Key Traits and Data Structures​

  • RiskLimit — a configured threshold (capital ratio, LCR, concentration, VaR) with breach state; crossing it emits bank8:risk:limit:breached.
  • Exposure — a measured position (counterparty, currency, asset class) updated incrementally from posting events.
  • CapitalComponents / LiquidityBuffers — Basel / LCR-NSFR bucket aggregations computed from the ledger.
  • EclModel — IFRS 9 expected-credit-loss staging (12-month vs. lifetime) driven by credit events.

Rationale, Trade-offs, and Alternatives​

  • Event-driven measurement — risk reacts to bank8:ledger:posting:created and bank8:payments:instruction:completed rather than polling; the event payload carries the full snapshot (account id + amount + posting id), minimizing read-back (principles §4.7, event-first).
  • Breach as an event, not a table poll — limits are monitored incrementally; a breach is a domain event Compliance and Reporting both consume, never a shared table grant.
  • Jurisdiction drives thresholds — capital/liquidity floors differ by regulator; they are registry data (CRR3/CRD6 output floor, OSFI CAR/LAR, US Basel III), not code.

See DESIGN.md for the wire-level detail and BUSINESS.md for the business capabilities.

Design attribution: bank8:risk and its underlying concepts were designed by Hamid Jahanzad Hamid@Jahanzad.com.